1. Field of the Invention
The present invention relates to audio control methods and audio processing systems, and more particularly, to an audio processing system with automatic gain adjustment based on an analog audio input signal.
2. Description of the Prior Art
Please refer to FIG. 1. In a conventional audio processing system 10, speakers 18 produce sounds when an analog audio source signal from an analog audio input source 12 is amplified by an amplifier 14 and the resulting analog audio signal drives the speakers 18. The amplifier 14, according to a control signal from a control device 16, adjusts the gain of the amplifier 14, so as to control the level of the audio signal, such that the speakers 18 can output the sound at different volumes.
However, in the conventional audio processing system 10, the gain range of the amplifier 14 is fixed. Typically, the gain of the amplifier 14 controlled by the control device 16 is set to a middle value of the range in advance. Then, based on audio signals with different signal amplitudes, a user can adjust the volume to an acceptable level via the control device 16. However, because the gain range of the amplifier 14 is fixed, a great deal of inconvenience can be caused if the audio signal is at an extreme signal amplitude. For example, when the audio input signal amplitude is extremely high, and the gain of the amplifier 14 is also set at the upper end of the gain range, the speakers 18 can be overloaded and burn out within just a short period of time. On the other hand, if the audio input signal amplitude is extremely low, even if the gain of the amplifier 14 is set at the highest value of the gain range, the volume at the speakers 18 may still be too low, and will be unable to satisfy the listener. In addition, when the analog audio input source 12 is not inputting an audio source signal, the conventional audio processing system 10 has no way of automatically entering a mute state, but must be manually adjusted by the user.